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The other way to make toroids

Original poster: "Wim Bosma" <wbosma@xxxxxxxxxxx>

Hello Jerry, If this prescription is overly long, you may snip in it. I also attach two small pictures of toroids in the process of making. Regards and keep up the good work! Willem.

Hello all,
I have made several toroids from plastic dryer duct. Its inside stiffener is a steel spiral. With a wire cutter you can snip it. Form a toroid by sewing both ends together. Then make a styrofoam disc, the size of the inner diameter of the toroid to be, about 1 to 2 inches thick and hollow the circumference a bit to fit the diameter of the ducting. Now you glue (epoxy or woodglue) upon it two thin discs of plywood (or aluminium) to make a stiff sandwich. You can stretch the formed toroid so it slips over the sandwiched styrofoam disc and stays in place. Try to stretch so that the formed outer diameter is as smooth as possible. Now comes the messy part... Tear newspapers to shreds and make paperpulp by boiling the shredded mass with water while stirring. After having a smooth paste, strain the excess water and stir some woodglue thru the paste. You can add fine woodmill to this paste. Now apply this paste to one side of the toroid, omitting the flat inner surface, forming a smooth surface and let it dry somewhat. Then turn over and prepare the other halve. After drying you can correct mistakes with another or smoother layer with more sawdust in it. Also you can use some filler from a paint store. After drying, sand protruding little coarsenesses away and apply a coating of some lacquer or Krylon. Now get a roll of aluminium repair tape that has a protective layer on the sticky side and cut off lengths equal to the circumference of the ducting and a little bit more. With a Stanley knife cut the straps lengthwise in two so you get the double number of straps with half the width. The smaller the width, the less trouble in wiping away wrinkles...Place straps carefully and symmetrically with respect to the two sides, with a small overlap on the outside of the toroid. Press down gently and then with a smooth flat wooden spatel flatten out the wrinkles. Aluminium tape deforms easily so you should end up without wrinkles...The last thing to do is glue aluminium discs on the flat sides that contact the repairstrips where they join and overlap each other.
Regards, Willem, PA0TW